In the Lippi lab, we use a reductionist approach to understand how molecules affect circuits formation and function.
During their life-span neurons undergo profound changes in gene expression that trigger rapid transitions in their developmental trajectory. The overarching goal of the research in my lab is to identify the key molecular players that drive and coordinate these transcriptional changes. In particular, we focus on non-coding RNAs (ncRNAs), a novel and exciting class of master regulators of gene expression. Intriguingly, recent discoveries suggest that the number of protein-coding genes has changed very little from unicellular to complex multicellular organisms. Instead, the increase in biological complexity derives from additional layers of regulation of gene expression provided by the expansion of the ncRNA repertoire. Many ncRNAs are enriched in the brain and increase their expression during development, suggesting that they play fundamental roles in establishing properly balanced neural networks. Consistently, recent literature indicates that changes in ncRNA levels are linked to multiple neurodevelopmental disorders, including autism, schizophrenia and epilepsy. However, how ncRNAs instruct proper neural networks development is not known.
We were the first to show that microRNAs (miRs), a class of ncRNAs, are master regulators of a critical developmental window, during which most synaptic connections are formed. Using an array of techniques, including single unit recording in freely moving animals, calcium imaging, electrophysiology, and behavioral studies, we demonstrated that even a temporary inhibition of specific miRs can trigger profound long-term consequences for network stability and function (Lippi et al. 2016). The changes include excessive synaptic activity, propensity for seizure-like activity, and memory impairments, recurrent pathological features shared by many neurodevelopmental disorders. Using a set of molecular tools for in vivo dissection of miRs function, we identified and parsed out the molecular pathways regulated by the miRs to achieve a properly balanced network. Interestingly, several of the miR targets identified had already been linked to specific features of neurodevelopmental disorders. Taken together, these findings suggest that miRs tightly regulate a core of highly interconnected developmental programs that control critical developmental windows. They also suggest that ncRNAs can be used as tools to understand the transcriptional organisation that instructs proper neural network formation and how this process can go wrong at the onset of diseases.
We have now developed a set of genetics tools that will allow us to ask much more sophisticated questions. Which miRs are enriched in different cell-types and what is the specific set of targets they regulate? What are the nodes where regulation of multiple miRs converge and why is redundant regulation necessary? What is the effect of selective removal of miRs from certain cell-types? Are miRs important for the development and function of these cell-types? What are the consequences for network activity and emerging cognitive functions? What is the function of other less known ncRNAs (circular RNAs, long non coding RNAS, piwi RNAs, etc.)? We are also very interested in a second set of questions that will be carried out in iPSC cells. What is the function of primate/human specific miRs? Are these miRs responsible for the increase in primates’ cognitive abilities?
Addressing these questions requires techniques that span from genetics, cellular/molecular neuroscience, to imaging of large ensembles of neurons in vivo, and behaviour.
Dulcis D.*, Lippi G.*, Stark C.J., Do L.H., Berg D.K., Spitzer N.C. (2017) Neurotransmitter switching regulated by miRNAs controls changes in social preference. Neuron. 95 (6): 1319-1333. *first author. DOI: http://dx.doi.org/10.1016/j.neuron.2017.08.023.
Lippi G., Fernandes C.C., Ewell L.A., John D., Romoli B., Curia G., Taylor S.R., Frady E.B., Jensen A.B., Liu, J.C., Chaabane M.M., Belal C., Nathanson J.L., Zoli M., Leutgeb J.K., Biagini G., Yeo G.W., Berg D.K. (2016) MicroRNA-101 regulates multiple developmental programs to constrain excitation in adult neural networks. Neuron. 92 (6): 1337-1351. DOI: 10.1016/j.neuron.2016.11.017.
Wang X., Lippi G., Carlson D.M., Berg D.K. (2013) Activation of a7-containing nicotinic receptors on astrocytes triggers AMPA receptor recruitment to glutamatergic synapses. J Neurochem. 27, 632–643. DOI: 10.1111/jnc.12436.
Saba R., Störchel P., Aksel A.A., Kepura F., Lippi G., Plant T.D., Schratt G.M. (2012) The dopamine-regulated microRNA, miR-181, controls GluA2 surface expression in hippocampal neurons. Mol Cell Biol. 32 (3): 619-32. DOI: 10.1128/MCB.05896-11.
Lippi G., Steinert J.R., Marczylo E.L., D’Oro S., Fiore R., Forsythe I.D., Schratt G., Zoli M., Nicotera P., Young K.W. (2011) Targeting of the ARPC3 actin nucleation factor by microRNA-29a and 29b regulates dendritic spine morphology. J Cell Biol. 194 (6): 889-904. DOI: 10.1083/jcb.201103006.
Ziviani E.*, Lippi G.*, Bano D., Munarriz E., Guiducci S., Zoli M., Young K.W., Nicotera P. (2011) Ryanodine receptor-2 upregulation and nicotine-mediated plasticity. EMBO J. 30 (1):1 94-204. DOI: 10.1038/emboj.2010.279. *first author.